The present invention relates to a device for separating a quadrature modulated composite video signal into a luminance signal and a color signal in a television receiver, and more particularly to a luminance/color signal separating device which separates a composite video signal into a luminance signal and a color signal according to spectrum distribution of luminance signal and color signal, thereby preventing dot trouble, deterioration of picture quality and vertical resolution.
In a quadrature modulated color television type such as an NTSC type and a
type, the composite video signal is composed of a luminance signal and a color signal interleaved in the luminance signal to minimize an occupied frequency band. The luminance signal and the color signal included in the composite video signal have spectrum distribution having large superposed region with each other in horizontal, vertical, and temporal frequencies, as a picture varies in horizontal, vertical, diagonal, and temporal directions. Accordingly, a luminance/color signal separating device used in a television receiver should separate the composite video signal into a luminance signal and a color signal according to the spectrum distribution of luminance signal and color signal.
However, the conventional luminance/color signal separating circuit separates the composite video signal into a luminance signal and a color signal by a line comb filter utilizing the characteristic of phase inversion of color signal in every line, or by a frame comb filter utilizing the characteristic of phase inversion of color signal in every frame, thereby causing the dot trouble, the deterioration of picture quality and vertical resolution.
In detail, when the composite video signal has a picture rapidly changed in a vertical direction, a color signal component is included in a luminance signal separated by the line comb filter and a luminance signal component is included in the separated color signal, so that the dot trouble, and the deterioration of picture quality and vertical resolution are generated by the color signal component and luminance signal component included in the separated luminance signal and the separated color signal, respectively. When the composite video signal has a picture varying in a temporal direction, a color signal component is included in a luminance signal separated by the frame comb filter and also a luminance signal component is included in a color signal separated by the frame comb filter, so that the dot trouble, the deterioration of picture quality and vertical resolution, etc. are generated by the color signal component and luminance signal component included in the separated luminance signal and color signal, respectively.
To solve the problems of the line comb filter and the frame comb filter, a motion adaptive luminance/color signal separating device is suggested. The motion adaptive luminance/color signal separating device comprises the line comb filter for separating the composite video signal into a luminance signal and a color signal according to the characteristic of the phase inversion of color signal per line, a frame comb filter for separating the composite video signal into a luminance signal and a color signal according to the characteristic of the phase inversion of color signal per frame, and a means for detecting a motion of picture from the composite video signal and switching the operation of the line comb filter and the frame comb filter according to the detected picture motion signal. However, the motion adaptive luminance/color signal separating device also has the problems of generating the dot trouble, and the deterioration of picture quality and vertical resolution by the color signal component and luminance signal component included in the separated luminance and color signals, when the motion of picture is incorrectly detected. And, when there is a picture motion, and the picture changes rapidly in a vertical axis direction, the luminance and color signals separated by the line comb filter include the color signal component and the luminance signal component, respectively, so that the motion adaptive luminance/color signal separating device cannot prevent the dot trouble, and the deterioration of picture quality and vertical resolution. These problems are described in detail with reference to the accompanying drawings as follows.
With reference to FIG. 1, a composite video signal of NTSC type including a luminance signal Y, and first and second chrominance signals I and Q is described. The luminance signal Y is distributed in a frequency band of 4.2 MHz, and the first and second chrominance signals I and Q are respectively distributed in frequency bands of approximately 1.5 MHz and 0.5 MHz from the centered chrominance subcarrier frequency, i.e., fsc=3.58 MHz.
FIG. 2 shows spectrums of luminance signal Y and color signal C distributed near a chrominance subcarrier frequency fsc shown in FIG. 1. The spectrum of luminance signal Y is repeatedly shown with a principal frequency nFn, and also the spectrum of color signal C is repeatedly shown with a principal frequency {(2n+1)Fn/2}. Accordingly, when a composite video signal has a picture rapidly changed in a vertical direction, the superposition between the spectrums of luminance signal Y and color signal C is severed. Here, n is an integer, and Fn is a line (horizontal sync signal) frequency. And, the line frequency Fn is 15.75 KHz, in case of an NTSC type.
FIG. 3 is a circuit diagram of a conventional comb filter. In FIG. 3, the conventional comb filter comprises a band-pass filter 12 for passing only a signal existing in a band of approximately 2 MHz to 4.3 MHz near a chrominance subcarrier frequency, i.e., 3.58 MHz, from a composite video signal CV received through an input terminal 10, a first delay 14 for delaying an output signal V1 of the band-pass filter 12, a second delay 16 for again delaying an output signal V2 of the first delay 14, first and second amplifiers 18 and 20 for amplifying the output signals V1 and V3 of the band-pass filter 12 and the second delay 16 by a half times, an adder 22 for adding output signals of the first delay 14 and the first and second amplifiers 18 and 20, and a third amplifier 24 for amplifying an output signal of the adder 22 by a half times. The comb filter shown in FIG. 3 is a 2H (here, H is a period of horizontal sync signal) comb filter if the delay period of the first and second delays 14 and 16 is one line period, and on the other hand, is a 2F (here, F is a period of frame) comb filter if the delay period of the first and second delays 14 and 16 is one frame period. The signal V1 filtered in the band-pass filter 10 is sequentially delayed in the first and second delays 14 and 16, thereby outputting signals V2 and V3. The output signal V1 of the band-pass filter 10 and the output signal V3 of the second delay 16 are amplified in the first and second amplifiers 18 and 20, and then are added with an output signal V2 of the first delay 14 by the adder 22. The third amplifier 24 amplifies an output of adder 22 by a half times, thereby obtaining an amplified signal V0=1/2(V2-1/2(V1+V3)).
At this time, if the signs of output signals of first and second amplifies 18 and 20 are negative, an output signal V0 becomes a color signal and contrarily, if the signs are positive, an output signal V0 becomes a luminance signal.
When a composite video signal having a picture rapidly changed in a vertical direction is inputted, the line comb filter having a line delay cannot exactly separate a luminance signal and a color signal, thereby generating an interference phenomenon between a luminance signal and a color signal, and deteriorating vertical. resolution of color signal. Also, the frame comb filter having a frame delay cannot exactly separate a composite video signal having a motion picture in motion into a luminance signal and a color signal, thereby deteriorating picture quality.
To improve such problems of comb filter, a motion adaptive luminance/color signal separating device shown in FIG. 4 is developed. The motion adaptive luminance/color signal separating device comprises a line comb filter 30 and a frame comb filter 32 for separating a composite video signal CV received through an input terminal 28 into a luminance signal and a color signal by the line correlation and the frame correlation, respectively, a motion detector 34 for detecting a motion of the composite video signal CV, and a mixer 36 for selecting output signals of the line comb filter 30 and frame comb filter 32 according to an output signal of the motion detector 13 and outputting the selected signal through an output terminal 38. In the conventional motion adaptive luminance/color signal separating device having the above constitution, a composite video signal CV inputted in the input terminal 28 is separated into a luminance signal and a color signal by the line comb filter 30 and the frame comb filter 32, and the separated signals are inputted to the mixer 36. The motion detector 13 detects a motion component from a composite video signal and supplies the detected motion signal as a control signal to the mixer 36. Then, the mixer 36 selects the luminance signal and color signal separated by the line comb filter 30 when a motion component exists in a composite video signal CV, and selects the luminance signal and color signal separated by the frame comb filter 32 when a motion does not exist.
However, the above-mentioned conventional motion adaptive luminance/color signal separating device relatively exactly separates a luminance/color signal when the motion component of composite video signal CV is exactly detected, but the picture motion component cannot be exactly detected from a composite video signal having mixed luminance signal and color signal. Accordingly, when a composite video signal having a motion component of picture is determined to have no motion, the conventional motion adaptive luminance/color signal separating device wrongly separates a luminance signal and a color signal from a composite video signal, thereby generating a rainbow pattern or dot trouble due to cross-color and cross-luminance components. And, when a composite video signal having no motion of picture is determined to have a motion component, the conventional motion adaptive luminance/color signal separating device generates the reduction and deterioration of resolution of color signal, and the deterioration of picture quality due to the interference between the luminance signal and color signal.